Thermal Distribution in District Energy and Cogeneration Systems

Transcription

1 International District Energy Association Thermal Distribution in District Energy and Cogeneration Systems Presented by William A. Liegois, P.E. Stanley Consultants, Inc.

2 Topics Principles of Hot Water Conversion to Hot Water Hot Water and Cogeneration Advantages of Hot Water

3 Basic Thermodynamics Energy degrades into lower levels Only provide energy at the level required by the user Providing lower level energy saves money Lower cost to produce More options for heat recovery Design buildings to operate on lowest level energy possible

4 Hot Water Classifications Low Temperature Systems (< 225 F) Medium Temperature Systems (226 to 350 F) High Temperature Systems (351 to 450 F)

5 Design Principles Pressurize System 15 to 25 psig Produce Water at a Design Temperature One-pump and Two-pump Systems Normal Differential Temperatures, 75 to 150 F Unfired Pressure Vessels Make Steam for End Users Applications are Campus-type Services

6 HW Properties High Density High Specific Heat Low Viscosity Good Thermal Conductivity Properties Materially Different than Steam

7 HW Properties (continued) Pressure Changes have Negligible Effect on Density Specific Heat Thermal Conductivity Temperature Changes have only a Small Effect

8 HW Design Parameters HTHW 300 lb class 425 F Upper Temperature LTHW 150 lb class 225 F Upper Temperature

9 HW Design Parameters (continued) Heat Content of One Cubic Foot Water from 400 F to 250 F = 7,266 Btu/ft 3 Water from 225 F to 150 F = 4,268 Btu/ft 3 Steam to Condensate at 400 F = 373 Btu/ft 3 Pressure Drops have Minimal Effect on HW Temperatures Heat Capacity Ratio

10 Typical Design Conditions High Temperature Hot Water (HTHW) Supply Temperature, F System Delta Temperature, 150 F Pressure, psig Low Temperature Hot Water (LTHW) Supply Temperature, F System Delta Temperature, F Pressure, psig

11 Two Pump System Nitrogen Pressurization

12 Installed Piping Comparison Basis of Design: 100 MMBtu/hr of heat in 1,000 feet of pipe with expansion joints and fittings. Steam Piping, 14 inch steam 4 inch condensate. Excavation 10% Pipe Installation 75% Surface Repair 15% HTHW, 8 inch supply & return. Excavation 15% Pipe Installation 70% Surface Repair 15% LTHW, 10 inch supply & return. Excavation 20% Pipe Installation 60% Surface Repair 20% Basis Cost 100 units Basis Cost 90 units Basis Cost 60 units

13 Piping Conversions All new distribution system or system expansion and building conversions. New and renovated buildings designed for hot water, remaining on steam distribution. Convert some or all distribution to hot water. Convert the Heating Plant to hot water or cogeneration.

14 Traditional Steam Distribution Steam to Campus Vent Condensate from Campus Steam BFW

15 Conversion from Steam to HW Renovate by area, if possible, so distribution loops can be converted to HW. Re-use steam pipe and install a second line for hot water return. Take advantage of other construction activities.

16 Steam Generation with Steam Dist. & Hot Water Buildings Heating Plant Steam to Campus Steam Bldg HTHW Supply Bldg HTHW Return Vent Condensate from Campus Condensate Steam BFW

17 Steam Generation with Steam & Hot Water Distribution Heating Plant Steam to Campus Steam Multi Bldg HTHW Supply Multi Bldg HTHW Return Vent Condensate from Campus Condensate Steam BFW

18 Steam Generation with Hot Water Distribution Only Heating Plant Steam Multi Bldg HTHW Supply Multi Bldg HTHW Return Vent Condensate Steam BFW

19 Hot Water Generation with Hot Water Distribution Heating Plant Hot Water Supply HW Secondary Pump Hot Water Return HW Primary Pump

20 Building Conversions New Buildings Designed for hot water or renovated buildings now designed for hot water but on a steam system.

21 Building Conversions Old Buildings Designed for steam but on a HTHW supply system.

22 Hot Water and CHP Reciprocating Internal Combustion Engine (RICE) LTHW Recover Exhaust and Jacket Water Aux firing is an option to increase heat recovery HTHW Exhaust heat recovery only JW, LO, and AC heat are wasted to air or cooling tower

23 University of Iowa Research Park Campus

24 UI Research Park Simplified Schematic Engine Exhaust Steam from Existing Boilers LTHW to New Campus Exhaust HR Unit Condensate Return Jacket Water Cooling LTHW from New Campus

25 UIC RICE CHP Operation Jacket Water Reciprocating Engine/ Generators (2) 12.6 MWe Jacket Water Heat Exchanger 8 MMBTU/h Recovery Heat Exchangers 30 MMBTU/h St. Ignatius School and Holy Family Church HTHWGs 200 Boilers MMBTU/h Heating System East Campus Buildings Remote Absorption Chiller 1350 RT West Campus Plant 37.2 MWe 69 kv Bus Line East Campus 3.8 M ft 2 29 Buildings Natural Gas Absorption Chiller 1000 RT Reciprocating Engine/ Generators (2) 7.6 MWe Exhaust Gas Chilled Water System East Campus Buildings Electric Centrifugal Chillers 6500 RT

26 Hot Water and CHP Gas Turbines Make HTHW /LTHW directly Make High Pressure Steam psig Aux Firing is an option to increase heat recovery Compressor Convert to HTHW/LTHW for distribution Compressor Air Fuel Air Fuel Combustor Combustor Power Turbine Power Turbine Exhaust Generator Exhaust Generator HRSG Condensate HW Generator Steam Turbine Generator Steam HW from Process HW Supply HW Return HW to Process

27 Hot Water and CHP Steam Boilers Backpressure steam turbine for power generation. Heat Exchanger for conversion to HW for distribution.

28 Steam and Electric Generation with Hot Water Distribution Heating Plant HP Steam Electricity LP Steam Hot Water Supply Vent Hot Water Return Condensate Steam BFW

29 Additional Services Requiring Steam Sterilizers Kitchens Laundries

30 Advantages of HW Minimum Leakage and Makeup Water Pump Seals and Valve Packing 0 to 1 Percent Makeup Elimination of Corrosion and Scaling In Generators and Heat Transfer Equipment In Valves, Piping and Fittings No Condensate Line Corrosion Negligible Water Makeup Requirements No Blowdown No Heating or Chemical Treatment of Makeup Water

31 Advantages of HW (continued) No losses from Flash-off (Typically 15 to 25% for Steam) Flexibility in pipe routing Reduced pipe expansion with LTHW No Losses from Lack of Condensate Return (Typically 10 to 25% in Campus Distribution) Leaking System Malfunctioning Traps

32 Advantages of HW (continued) Reduced Water Treatment Equipment No Blowdown Closed Loop (100% Return) Low Head/High Volume Pumps Replace Boiler Feedwater Pumps Improved Heat Storage in System Hot water normally results in improved overall system efficiency at installed costs similar to or less than a steam system.

33 Thank you